Everyone know that "shit" should only be used in the adjective form not the noun
ie. "I just made a shitty poo" is good, however
"I just made a shit" is completely wrong and rude

Shit can be used for things other than toilet humour and toiletry actions
ie. "that was a shitty bus journey" is good, but
"that bus journey was like shit" is using the adjective "shit" in the wrong form